This application relates to refrigerant handling systems and, in particular, to systems for recovering and recycling refrigerant from cooling systems, such as those of automotive vehicles. The application relates in particular to techniques and apparatus for purging non-condensables from the recovered refrigerant.
As used herein, xe2x80x9crecoverxe2x80x9d means to remove used refrigerant from a refrigeration system and collect it in an appropriate external container or vessel. xe2x80x9cRecyclexe2x80x9d means to reduce the amount of contaminants in used refrigerants so that it can be reused.
During service or repair of refrigeration systems, such as automotive vehicle air-conditioning systems, the refrigerant charge in the refrigeration system is recovered and recycled, both to avoid pollution of the atmosphere and to minimize the increasing costs of disposal and replacement of the refrigerant charge. One type of impurity which must be removed from recovered refrigerant is non-condensable material, such as air, which can infiltrate the refrigeration system as a result of leaks or the like. The non-condensables can be vented to atmosphere, but care must be taken that, in the process, minimal refrigerant is vented, in order to ensure compliance with governmental pollution control regulations. It is known that refrigerants have characteristic saturation vapor pressures that vary as associated functions of temperature, as long as refrigerant is present in both liquid and vapor phases, such as in the refillable recovered refrigerant vessel of a refrigerant recycling system. If air or other non-condensables are present in the recovered refrigerant vessel, a differential pressure above the saturation pressure is created, which is proportional to the quantity of non-condensables present. This relationship is used for automatically venting the non-condensables. More specifically, an ideal pressure of the refrigerant at a given temperature is determined and, when the actual measured pressure of the refrigerant exceeds that ideal, a venting valve is opened. One such arrangement is disclosed, for example, in U.S. Pat. No. 5,369,959, the disclosure of which is incorporated herein by reference.
In the recovery vessel the recovered refrigerant exists both in liquid and gaseous phases. During recovery, the temperature of the gases at the top of the vessel increase, compared to the liquid in the vessel and also compared to the ambient air around the vessel, due to the heat of compression as the refrigerant gases are drawn through the compressor of the recovery system. In current high-performance recovery systems, the temperature of the gases in the tank may be significantly higher than the air temperature of the air surrounding the tank, and the tank wall itself, on which the temperature sensor is mounted. Thus, the temperature measured by the temperature sensor at the end of a recovery operation will be artificially low, resulting in a correspondingly low ideal vapor pressure and, accordingly, a wider pressure gradient between the measured pressure and the ideal pressure than actually exists, leading the system to conclude that more purging is required than necessary. This can lead to reduced efficiency of the recovery process due to over-purging.
If more time were allowed to pass before the purge process was started, the temperature of the gasses in the vessel would eventually drop to a value closer to that of the ambient air around the tank, decreasing the temperature gradient, so that the measured temperature would more accurately reflect the actual temperature of the gases, but during this time delay, some of the non-condensable gases would be allowed to be absorbed into the liquid refrigerant, which is undesirable.
This application discloses a refrigerant recycling system with an improved non-condensable purge control which avoids the disadvantages of prior systems while affording additional structural and operating advantages.
An important aspect is the provision of a purge control technique which is effective with modem high-performance refrigerant recycling systems.
Another aspect is the provision of a purge control technique which can effectively and rapidly purge substantially all non-condensables in a recovered refrigerant volume while minimizing risk of over-purging.
Still another aspect is the provision of a purge control technique of the type set forth, which purges to a target pressure which is offset from the ideal vapor pressure corresponding to the measured temperature of the recovered refrigerant.
Certain ones of these and other aspects may be attained by providing apparatus for purging to atmosphere non-condensables from a volume of refrigerant, the apparatus comprising: a pressure transducer coupled to the volume for measuring the pressure therein; a temperature transducer disposed for measuring the temperature of gas in the volume; a purge valve coupled between the volume and atmosphere and operable between a closed condition isolating the volume from atmosphere and an open condition permitting exposure of the volume to atmosphere; and a processor operating under control of a stored program for controlling operation of the valve, the program including a purge routine responsive to measured temperature of the volume for determining an ideal vapor pressure in the volume corresponding to the measured temperature, the purge routine being responsive to measured pressure in the volume exceeding a target pressure above the ideal vapor pressure for effecting a controlled operation of the purge valve until the measured pressure drops to the target pressure.
Other aspects may be attained by providing apparatus of the type set forth in a refrigerant recovery system, and purging to the offset target pressure at the conclusion of a recovery operation and then purging to a non-offset target pressure at the beginning of the next succeeding recovery operation.